Peter J. Lovell disclosed a protective helmet in his U.S. Pat. No. 4,307,471 by providing a plurality of projections (25) between an outer shell (21) and an inner shell (22). Since the projections (25) are substantially rigid, the helmet as being subjected to a serious external impact force would not effectively dampen the external force, thereby still being dangerous to a helmet wearer.
Leonard P. Frieder et al. disclosed a custom-fitted helmet in their U.S. Pat. No. 4,345,338 incorporating sack (12) containing resin-bead composite (20) in the inner sheet (16) inside the outer sheet (14) and a plurality of molding extrusions (30, 32, 34 and 36) inserted in between the outer and inner sheets, thereby forming a helmet filled with almost "solid" matters in between the outer and inner sheets 14, 16 to increase a weight worn by the wearer and to reduce air penetrable space to influence ventilation within the helmet to easily cause uncomfortableness and tiredness to the wearer.
The present inventor has found the drawbacks of the conventional helmets and invented the present safety helmet with bellows cushioning device.